1. Field of the Invention
The invention relates to a radiation image recording and read-out apparatus for exposing stimulable phosphor sheets respectively to a radiation passing through an object to have a radiation image of the object stored thereon, exposing the respective stimulable phosphor sheets to stimulating rays which cause them to emit light in proportion to the stored radiation energy, and detecting and converting the emitted light into electric signals. This invention particularly relates to a radiation image recording and read-out apparatus in which the stimulable phosphor sheets are reused for radiation image recording.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428, and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet comprising the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object to have a radiation image stored therein, and is then scanned with stimulating rays which cause it to emit light in proportion to the radiation energy stored. The light emitted from the stimulable phosphor sheet when the sheet is exposed to the stimulating rays is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image having an improved quality, particularly a high diagnostic efficiency and accuracy. The finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). In this radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store the radiation image in order to reproduce the final visible image therefrom in a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheet be used repeatedly.
Further, in a mobile X-ray diagnostic station such as a traveling X-ray diagnostic station in the form of a vehicle like a bus which is provided with a radiation image recording and read-out apparatus for use in the aforesaid radiation image recording and reproducing system and moves from place to place to record radiation images for mass medical examinations, it is disadvantageous to load the mobile X-ray diagnostic station with a large number of stimulable phosphor sheets, and the number of the stimulable phosphor sheets which can be loaded on the mobile X-ray diagnostic station is limited. Therefore, it is desired to load the mobile X-ray diagnostic station with stimulable phosphor sheets which can be used repeatedly, store the radiation images of the objects first in the stimulable phosphor sheets, transfer the electric image signals read out from the stimulable phosphor sheets into a recording medium having a large storage capacity, such as a magnetic tape, and circulate and reuse the stimulable phosphor sheets for further image recording and read-out operations, thereby to obtain the radiation image signals of many objects. Further, when image recording is conducted continuously by circulating and reusing the stimulable phosphor sheets, it becomes possible to increase the image recording speed in mass medical examination. This is very advantageous in practical use.
In order to reuse stimulable phosphor sheets as described above, the radiation energy remaining in the stimulable phosphor sheet after it is scanned with stimulating rays to read out the radiation image stored therein should be erased by exposure to light or heat as described, for example, in Japanese Unexamined Patent Publication No. 56(1981)-12599 or U.S. Pat. No. 4,400,619. The stimulable phosphor sheet should then be used again for radiation image recording.
From the aforesaid viewpoint, the applicant proposed in Japanese Unexamined Patent Publication No. 59(1984)-192240 a built-in type radiation image recording and read-out apparatus comprising:
(i) a circulating and conveying means for conveying at least one stimulable phosphor sheet for recording a radiation image thereon along a predetermined circulation path,
(ii) an image recording section positioned on said circulation path for recording a radiation transmission image of an object on said stimulable phosphor sheet by exposing said stimulable phosphor sheet to a radiation passing through said object,
(iii) an image read-out section positioned on said circulation path and provided with a stimulating ray source for emitting stimulating rays for scanning said stimulable phosphor sheet carrying said radiation image stored therein in said image recording section, and a photoelectric read-out means for detecting light emitted from said stimulable phosphor sheet scanned with said stimulating rays to obtain an electric image signal, and
(iv) an erasing section for, prior to the next image recording on said stimulable phosphor sheet for which the image read-out has been conducted in said image read-out section, having said stimulable phosphor sheet release the radiation energy remaining in said stimulable phosphor sheet, whereby said stimulable phosphor sheet is circulated through said image recording section, said image read-out section and said erasing section and reused for radiation image recording. With the radiation image recording and read-out apparatus of this type, it is possible to conduct radiation image recording and read-out continuously and efficiently.
In the aforesaid radiation image recording and read-out apparatus, for example, when it is found that the radiation image recording at the image recording section was incorrect, it is desired to send the stimulable phosphor sheet, which was subjected to the radiation image recording, directly to the erasing section without conducting image readout to erase the stored radiation energy, thereby quickly making the sheet reusable for image recording. Also, when there are stimulable phosphor sheets on which image recording has been conducted but image read-out has not been carried out, it is often desired to conduct urgent image recording and read-out on a stimulable phosphor sheet preferentially to the aforesaid stimulable phosphor sheets and quickly observe the radiation image. Further, in the case where a stimulable phosphor sheet is left to stand for long periods without being used for radiation image recording after erasing at the erasing section, i.e. releasing of residual radiation energy, is carried out on the sheet, the sheet may store radiation energy constituting a noise component caused by floating-off of residual image or the like. Therefore, in such a case, instead of directly using the stimulable phosphor sheet for the next radiation image recording, it is desired to send the stimulable phosphor sheet to the erasing section to carry out erasing (secondary erasing) and make it reusable for the next radiation image recording.
However, with the aforesaid radiation image recording and read-out apparatus, since the image recording section, the image read-out section, and the erasing section are positioned along the sheet circulation path, the stimulable phosphor sheet must be sequentially passed through the respective sections for returning to the erasing section even though the radiation image recording and/or read-out should be skipped for the sheet. Therefore, a long time is taken for the sheet circulation, and the waiting time becomes long. Also, since processing is possible only in the image recording sequence, it is not possible to conduct urgent processing preferentially.